566 THE STRUCTURE AND DEVELOPMENT 



These figures should be compared with those of the table on 

 page 564. 



The ova when first formed are situated either at the surface 

 or in the deeper layers of the germinal epithelium. Though to a 

 great extent surrounded by the ordinary cells of the germinal 

 epithelium, they are not at first enclosed in a definite follicular 

 epithelium. The follicle is, however, very early formed. 



My observations lead me then to the conclusion that in 

 a general way the permanent ova are formed by the increase of 

 protoplasm round some of the nuclei of a nest, and the subse- 

 quent separation of the nuclei with their protoplasm from the 

 nest as distinct cells a mode of formation exactly comparable 

 with that which so often takes place in invertebrate egg tubes. 



Besides the mode of formation of permanent ova just de- 

 scribed, a second one also seems probably to occur. In ovaries 

 just younger than those in which permanent ova are distinctly 

 formed, there are present primitive ova, with modified nuclei of 

 the stellate variety, or nuclei sometimes even approaching in 

 character those of permanent ova, which are quite isolated and 

 not enclosed in a definite nest. The body of these ova is formed 

 of granular protoplasm, but their outlines are very indistinct. 

 Such ova are considerably larger than the normal primitive ova. 

 They may measure 0^04 mm. In a slightly later stage, when 

 fully formed permanent ova are present, isolated ones are not 

 infrequent, and it seems natural to conclude that these isolated 

 ova are the direct descendants of the primitive ova of the earlier 

 stage. It seems a fair deduction that in some cases primitive 

 ova undergo a direct metamorphosis into permanent ova by a 

 modification of their nucleus, and the assumption of a granular 

 character in their protoplasm, without ever forming the con- 

 stituent part of a nest. 



It is not quite clear to me that in all nests the coalescence 

 of the protoplasm of the ova necessarily takes place, since some 

 nests are to be found at all stages in which the ova are distinct. 

 Nevertheless, I am inclined to believe that the fusion of the ova 

 is the normal occurrence. 



The mode of formation of the permanent ova may then, 

 according to my observations, take place in two ways : I. By 

 the formation of granular protoplasm round the nucleus in a 



